1. Field of the Invention
The present invention relates generally to magnetic transmissions and, more specifically, to magnetic transmissions which utilize rotatable planetary members disposed in on contact torque transmitting relation with both a rotatable sun member and a rotatable ring member. Each of the rotatable members is provided with a plurality of magnetic poles which comprise alternating north and south magnetic polarities.
2. Description of the Prior Art
In many different types of applications, it is necessary to isolate the driving member of a transmission from the driven member of a transmission. For example, the driving member may be surrounded by a first fluid and the driven member may be surrounded by a second fluid in an application where the first and second fluid must be isolated from each other. This type of requirement necessitates the physical separation and fluid isolation of the driving and driven members. To solve this type of problem, noncontact magnetic driving members can be used with a nonmagnetizable diaphragm disposed between the driving and driven members to isolate them from each other and any fluids with which they may individually be associated.
U.S. Pat. No. 3,649,137, which issued to Laing on March 14, 1972, describes a centrifugal pump with a magnetic coupling. It incorporates a motor driven centrifugal pump with a magnetic transmission that comprises a permanent magnet pole ring and a soft iron magnetic pole ring, whereby means are provided for reducing the magnetic slots which determine the torque and which flows through the two pole rings.
U.S. Pat. No. 4,115,040, which issued to Knorr on Sept. 19, 1978, describes a permanent magnet pump which comprises a pump impeller and an interior rotor of a permanent magnet driving device that receives drive torque transmitted in synchronism from an exterior rotor. The exterior rotor is positioned, axially in one form and radially in another form, opposite the interior rotor with an air gap defined between them. Thin, plate-like permanent magnets carried by the rotors face each other across the air gap. The pump impeller shaft and the interior rotor are housed and supported in a common space which is sealed from the exterior by a partition of non-magnetizable material extending through the air gap.
U.S. Pat. No. 3,826,938, which issued to Filer on July 30, 1974, shows a magnetic coupling for a motor driven pump. The magnetic drive coupling of this patent can be employed in motor driven pumps and for other purposes, which include coupling members forming part of the magnetic circuit which can be isolated to prevent fluid communication therebetween and in which a plurality of stationary electrically activated flux sources are provided which also form part of the magnetic circuit and in which an improved flux path is provided.
United States Patent 3,378,710 which issued to Martin on April 16, 1968, discloses a magnetic transmission. It describes a magnetic drive that is similar to a planetary gear mechanical drive but with bars instead of rotatable gears in the planet positions. An outer ring magnet, an intermediate planet ring with a plurality of substantially radially magnetically permeable bars and a sun magnet all have a common axis of revolution. One of the elements is power driven and a second element is driven by the magnetic transmission. Either a speed increase or a speed decrease may be achieved with this device.
U.S. Pat. No. 4,850,821, which issued to Sakai on July 25, 1989, discloses a multiple magnet drive pump. Several embodiments of rotatable magnetic components are shown wherein a relatively large ring magnet is associated with a plurality of smaller planet magnets. The embodiments described in this patent dispose the planet magnet both radially outward from and radially inward from the ring magnet.
U.S. Pat. No. 4,725,197, which issued to Russell et al on Feb. 16, 1988, describes a device for imparting rotary motion. One embodiment of this device comprises a down-hole signal transmitter that includes an annular impeller mounted on a cylindrical casing and arranged to be driven by the mud flow passing along a drill string. Each of the impeller and the casing incorporates two sets of magnets with their poles arranged axially relative to one another such that axial movement of the impeller in one direction will tend to be resisted by a force of magnetic repulsion acting between the first set of casing magnets and the second set of impeller magnets and axial movement of the impeller in the opposite direction will tend to be resisted by a force of magnetic repulsion acting between the second set of casing magnets and the first set of impeller magnets. The magnetic coupling between the magnet sets enables driving torque to be transmitted by the impeller to a rotary drive member on which the casing magnets are mounted.
An article, entitled "Magnetic Coupling Delivers Increased Torque" is provided by the National Aeronautics and Space Administration and is identified by number MSC-21171 of the NASA Tech Briefs. This article and additional information regarding research and technology in the general area of magnetic couplings can be found in the Scientific and Technical Aerospace Report (STAR) which is a comprehensive abstracting and indexing journal covering world wide report literature on the science and technology of space and aeronautics. This particular article discusses a magnetically coupler for torque transmission that magnetic couples a rotating drive shaft to a driven shaft across a fluid boundary and allows space in the air gap for placement of other devices, such as fluid conduit, electrical conductor or other component without a great loss of efficiency.
When magnetic transmissions are used in speed reducing or speed increasing applications, the different sizes of driving and driven rotatable members that are required create certain problems which must be addressed. First, steps must be taken to assure that the air gap between the driving magnetic poles and the driven magnetic poles is not excessive to the degree which would reduce the strength of the magnetic coupling between these poles and permit slip to occur between these members which would adversely affect synchronism between the driving and driven members. If the smaller rotatable member is located externally adjacent the outer circumference of the larger rotatable member, the size requirements necessary to house the device must include the sum of the two diameters. If the smaller rotatable member is disposed within the inner circumferential dimension of the larger rotatable member and the two members must be concentric, some means must be taken to minimize the deleterious effect of a large air gap between the driving and driven magnetic poles which may differ significantly in size. The patents described above address these problems in several different ways. The present invention is particularly directed to solving the problem in speed reducing or speed increasing magnetic transmission couplings by reducing the overall required size of the transmission and by decreasing the air gap between the driving and driven magnetic poles so that increased torque can be transmitted without the need to significantly increase the size of the magnetic poles. The present invention is also directed to the provision of a plurality of intermediate rotatable magnet members to transmit torque between a driving member and a driven member. By providing a plurality of intermediate members, the intermediate members share the torque that is transferred between the driving and driven members and, as a result, the overall torque that can be transmitted through the transmission is proportionally increased in relation to the number of intermediate magnets used.